This invention relates to transgenic animals.
It is possible to insert foreign genes into vertebrate embryos, and for these genes to be incorporated into the genome of the resulting animal. Insertion of the foreign genes has been carried out mechanically (by microinjection), and with the aid of retrovirus vectors (for example, as is described in Huszar et al. (1985) P.N.A.S. U.S.A 82, 8587). The animals resulting from this process are termed “transgenic.” The foreign genes can be sexually transmitted through subsequent generations and are frequently expressed in the animal. In some instances the proteins encoded by the foreign genes are expressed in specific tissues. For example, the metallothionein promoter has been used to direct the expression of the rat growth hormone gene in the liver tissue of transgenic mice (Palmiter et al., 1982 Nature 300:611). Another example is the elastase promoter, which has been shown to direct the expression of foreign genes in the pancreas (Ornitz et al., 1985 Nature 313:600). Developmental control of gene expression has also been achieved in transgenic animals, i.e., the foreign gene is transcribed only during a certain time period, and only in a particular tissue. For example, Magram et al. (1985, Nature 315:338) demonstrated developmental control of genes under the direction of a globin promoter; and Krumlauf et al. (1985, Mol. Cell. Biol. 5:1639) demonstrated similar results using the alpha-feto protein minigene.